1. Field of the Invention
The present invention generally relates to the field of fiber optic circulators. More particularly, the present invention relates to the field of compact, low cost and high performance optical circulators, which can expanded to any number of ports.
2. Description of the Prior Art
The fiber optic circulator transfers light from a port to another sequentially. It is a passive optical junction of three or more ports. The ports can be accessed in such order that when a light beam is fed from an optical fiber to any port it is transferred to the next port. Typically, a light beam enters the circulator through a first port and exits through a second port. Another light that enters the second port exits through a third port and so on. Since the optical circulator is an inherently non-reciprocal device, the light never goes to other ports.
Such an optical device has a broad range of applications in the field of fiber optic communication systems, such as in bi-directional communication, dense Wavelength Division Multiplexing (WDM) and Dispersion Compensation.
Many types of optical circulators have been developed and manufactured. However, the high cost and bulky size of the circulator have limited the popular acceptance for system applications.
The present invention is a novel and unique fiber optic circulator which consists of two identical modules and one (for three port) or two (for four port) angles adjustor that allow two optical fibers to share one collimator lens and one birefringent crystal to achieve compactness and low cost.
In summary, a light beam is fed into the fiber of the first port in a dual fiber glass capillary, then collimated before being passed to a birefringent crystal wherein the light beam is divided into tow orthogonal components o and e with a displacement. The light beams of components then pass through the first Faraday Rotator that rotates the State of Polarization (SOP) of both components counterclockwise 45xc2x0. The components then pass into two Half-Wave Plates (HWP) that cover o and e components respectively.
One HWP is set 22.5xc2x0 against to horizontal for the e component and another one is set xe2x88x9222.5xc2x0 against to horizontal for the o component. The two components are in the same SOP in horizontal direction after the HWP. Then the light components pass into a birefringent prism which bents the light beams to be parallel to central axis of the circulator without displacement due to their SOP.
This is followed by a second pair of half wave plate, which changes the SOP of two components 45xc2x0 in opposite directions. This is followed by the Faraday rotator which rotates the components into orthogonal, the same as that after the first birefringent crystal. The light beam of components then pass into the second birefringent crystal which combines the o and e components together and pass through collimator lens, and are received by optical fiber of the second port.
The optical path from the second port to the third port is similar to that described above. However, due to the non-reciprocal property of the Faraday rotator, the SOP of the two light components from the second port will be perpendicular to the horizontal after Faraday rotator and half wave plates therefore receive a displacement after the walk-off birefringent crystal. This displacement the angle correction provided by the crystal prism allows that the light from the second port is fed into the fiber of the third port.
Further novel features and other objects of the present invention will become apparent from the following detailed description, discussion and the appended claims, taken in conjunction with the drawings.